Sympatric breeding of Sarus Cranes (Antigone
antigone) and Brolga (A. rubicunda)
occurs only in northern Queensland, Australia but factors contributing to this
unique sympatry are unknown. Large-scale developments currently planned in this
region, with potentially major impacts on cranes, create an urgent need to understand
the ecological requirements of each crane species. We carried out a multi-floodplain
landscape-scale survey during April-May 2017 and derived metrics for several ecological
aspects for the first time for both crane species. The abundance of the two
species differed between the floodplains. Both crane species synchronised
nest-initiation with rainfall (November to March). Breeding success was higher
than past estimates anywhere, with 60% of Sarus Crane pairs and 50% of Brolga
pairs fledging chicks. Sarus Cranes preferred four riverine Eucalyptus-dominated regional
ecosystems, with 10% using open habitats. Brolgas preferred two non-wooded
regional ecosystems, but 32% shared Eucalyptus-dominated
regional ecosystems with Sarus Cranes. Stable isotope analyses revealed Sarus diet
to be comprised of more diverse vegetation than Brolgas, while Brolgas fed across
a wider range of trophic levels. The ecology of Gulf cranes closely matched
habits of Sarus Cranes in south Asia, despite disparate conditions suggesting
considerable species plasticity. The diverse habitats of the Gulf and varying diet
appear to facilitate the cranes’ sympatry, and our study provides basic data
for developing long-term conservation plans in the face of development
activities.

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